1. Field of the Invention
This invention relates to data transfers between devices on a high speed digital network, and more particularly to a system and method for receiving an audio/visual multicast source on a high speed local or wide area packet network.
2. Description of the Background Art
In recent years, digital video data transmission over a local area network (LAN) has become more common. Before analog video data is transferred onto the LAN, analog video is converted to digital format. Available accessory hardware and software receive broadcast video programming and convert the analog video into digital format. Other hardware and software compress the digital format to digital video data that can be efficiently transferred to a personal computer or data network. Analog video data includes video programming material that is broadcast live, current programming broadcast on a television network, or pre-recorded programming. Often times, many devices monitor the transmission of the video programming that is broadcast onto the LAN.
In order to transmit digital video data over a data network, an effective transfer scheme for sending and retrieving the video data is required for the data network. Most data networks support three basic transfer schemes: a unicast addressing scheme where data is sent to one unique device on the data network, a broadcast addressing scheme where data is sent to all devices on the data network, and a multicast addressing scheme where data is sent to a group of devices on the data network. Each type of addressing scheme has characteristics that are both desirable and undesirable.
The unicast addressing scheme works well in a network system where only one output device receives the digital data from the data network. If there is a requirement that multiple output devices receive the digital data, then the source device has to retransmit the digital data for each additional output device. As the number of additional output devices increases, the data network quickly becomes overloaded and congested.
The broadcast addressing scheme permits multiple output devices to receive the digital data without requiring the source device to transmit multiple sets of digital data. However, the broadcast digital data is also transmitted to devices that are not interested in the digital data These devices have to receive the digital data and reject it. Thus, the broadcast of digital data onto the data network affects other devices on the data network. The problem is compounded when routers or network bridges are required to broadcast the digital data needlessly to neighboring data networks.
The multicast addressing scheme enables the transmission of digital data to be received by a select group of output devices on the data network system. Digital data is only received by the output devices that are interested in receiving the digital data. Available network adapters provide high speed filtering of multicast addresses for high performance rejection/selection of multicast addresses. Thus, a multicast addressing scheme is suitable for the selective transmission of digital data. However, the multicast addressing scheme has drawbacks when the scheme is used to transmit digital video programming.
Audio and video digital data converted for transfer on the data network include descriptive control information that has to be received by the receiving output device before the digital video data can be processed for output. In a unicast addressing scheme, the receiving output device can acknowledge the receipt of the descriptive control information before the source device proceeds to transmit the digital video data. In a multicast addressing scheme on an unreliable or lossy network, the source device does not receive acknowledgment signals from receiving output devices. The source device transmits digital video data onto the data network without regard to whether receiving output devices can receive and process the digital video data. Therefore, it is desirable to design a data network for receiving digital video data from a multicast addressing scheme that provides efficient transfer of digital video data which improves and overcomes the disadvantages of the prior art. The improved multicast addressing scheme should permit receiving devices to tap into and receive the multicast digital video data on the data network.